The present invention relates to latching mechanisms for the door of a household appliance such as clothes washing machine, and, in particular, to an electrically actuated lock for such a latch.
Appliances such as clothes washing machines and dishwashers may operate automatically through one or more cycles under the control of an automatic timer. During cycles when the consumer might be exposed to spraying water or hazardous moving parts, the door to the appliance may be locked by an electrical signal from the timer. The locking mechanism may, for example, insert a blocking member into a portion of the door latch to prevent it from being disengaged through the normal operation of the latch or may insert a blocking member directly into the door.
The locking mechanism may be actuated by an electrical solenoid having an element that moves through a conductive coil when electrical power is applied to the coil. Alternatively, electrical actuators, such as wax motors and heated bimetallic strips, may be used.
Each of the above mechanisms requires continuous power to remain actuated, typically for the duration of the locked cycle. In the case of a solenoid, this continuous duty requires increased size and expense of the coil windings which must be rated for continuous duty. A disadvantage of wax motors and bimetallic strips is that they rely on a heating process and thus cannot provide rapid locking and unlocking.
These disadvantages can be overcome through the use of an electromagnetically driven bi-stable actuator. Such an actuator may include a bidirectional solenoid that may either push or pull an actuator element depending on polarity of applied electrical power or power being applied to one of two coils. An over-center spring mechanism holds the actuator element in its last position, either locked or unlocked, when power is not applied.
During shipment of an appliance with a bi-stable lock, transportation shocks may cause the lock to move without the application of electrical power, for example, from the unlocked position to the locked position. This unintended locking of the appliance door can be inconvenient for the end user who may need access to the interior of the appliance before the appliance is installed and connected to electrical power, for example, to obtain parts or appliance manuals from the interior of the appliance.
This inadvertent actuation of the bi-stable lock can be eliminated by increasing the force of the over-center spring or adding frictional elements to the latch. This approach, however, necessitates a larger electromagnetic actuator, defeating to some extent the motivation for using a bi-stable actuator. Frictional elements can be difficult to manufacture so that they provide a consistent friction over the life of the product.